Generalized circuit model for analysis of extraordinary transmission in multilevel slits.

We propose a generalized circuit model for accurate analysis of the extraordinary transmission phenomenon in multilevel stepped slit structures. The multilevel stepped slit consists of some continuous sub-wavelength metal slits with different widths. By applying the proposed circuit model, we study the extraordinary transmission property of this structure for the two cases of ideal and real metal structures. The accuracy of the achieved results is validated by a full wave analysis based on the finite element method. Additionally, since the multilevel slit structure is adjustable by simply manipulating slit parameters such as widths and heights, various kinds of transmission spectra and a different number of resonance points are investigated by the circuit model and the numerical approach. Multilevel stepped slits can be used potentially as bandpass filters or optical attenuators in photonics integrated circuits.

Average bit error rate and channel capacity of terahertz wireless line-of-sight links with pointing errors under combined effects of turbulence and snow.

The estimation of the performance of terahertz wireless communication under the effect of various weather conditions is vital. In this work, the combined effects of cold weather conditions such as snow, as well as random effects of turbulence and pointing errors (PEs) between the transmitter and receiver, on the performance of terahertz wireless line-of-sight links have been evaluated. The exponentiated Weibull distribution has been employed to derive exact analytical closed-form expressions in the presence of combined channels. Our predictions indicate that snow can have various influences on the average bit error rate (BER) and the average channel capacity of terahertz wireless links. Dry and wet snow, based on its liquid-water content, shows different effects in terms of link parameters such as distance and frequency compared to that of rain. Random turbulence and PEs further deteriorate the link performance. It is concluded that the channel capacity is less affected than the BER under the effects of turbulence and PEs, while snow can have a remarkable effect. All of the predictions through the derived expressions are validated using Monte Carlo simulations.

Tunable compression of THz chirped pulses using a helical graphene ribbon-loaded hollow-core waveguide.

Pulse shaping is important for communications, spectroscopy, and other applications that require high peak power and pulsed operation, such as radar systems. Unfortunately, pulse shaping remains largely elusive for terahertz (THz) frequencies. To address this void, a comprehensive study on the dispersion tunability properties of THz chirped pulses traveling through a dielectric-lined hollow-core waveguide loaded with a helical graphene ribbon is presented. It is demonstrated that there is an optimal compression waveguide length over which THz chirped pulses reach the maximum compression. The optimal length is dependent on the chirp pulse duration. It is shown that by applying an electrostatic controlling gate voltage (Vg) of 0 and 30 V on the helical graphene ribbon, the temporal input pulses of width 8 and 12 ps, propagating through two different lengths, can be tuned by 5.9% and 8%, respectively, in the frequency range of 2.15-2.28 THz.

Generalized circuit model for all-dielectric narrowband metasurface absorbers.

All-dielectric metasurface absorbers have great potential in many scientific and technical applications. The emerging metasurfaces show strong and versatile capabilities in controlling absorptance, reflectance, and transmittance of electromagnetic waves. In this work, we propose and investigate all-dielectric metasurface absorbers with an equivalent circuit model. In the proposed circuit model, we satisfy the first Kerker condition. To verify the accuracy of the proposed model, the obtained results for an all-dielectric cubic metasurface absorber are compared with the existing experimental data. Moreover, using the proposed circuit model, we propose a hemisphere structure and compare the results of the proposed model with those of full-wave simulations. With this novel structure, we achieve higher absorptance and quality factor in comparison to a cubic one. Additionally, our proposed model reduces the calculation time and needs less memory compared to full-wave simulations. The results of the circuit model have an acceptable agreement with the experimental data and those of full-wave simulations. The proposed circuit model is simple yet general. It provides physical insight into the design and operation of various sub-wavelength structures in the broad frequency range, including THz and visible regions.